1. Field of the Invention
The present invention relates to a rotor and a motor.
2. Description of the Related Art
A so-called inner rotor type motor in which a rotor is disposed inside an armature is known. The types of rotors used in the inner rotor type motor are mainly classified into an SPM (Surface Permanent Magnet) type rotor in which a plurality of magnets are attached to the outer circumferential surface of a rotor core and an IPM (Interior Permanent Magnet) type rotor in which magnets are buried in a rotor core.
When the SPM type rotor is used, the armature and the magnets can be placed in proximity to each other. Therefore, the magnetic force of the magnets can be effectively used. However, in the SPM type rotor, measures to prevent the magnets from escaping outward due to a centrifugal force during high-speed rotation need to be prepared. On the other hand, when the IPM type rotor is used, there is no concern of the magnets escaping due to the centrifugal force. Therefore, recently, the IPM type rotor has been the mainstream type of rotor used.
However, in general, in any of the SPM type and IPM type rotors, each of the magnets is disposed so that a pair of magnetic pole surfaces are respectively directed radially outward and radially inward. Therefore, only the magnetic pole surface on the radial outside of the magnet contributes to motor driving. Here, recently, in order to effectively use the pair of magnetic pole surfaces of the magnet, a rotor structure in which magnets and cores of magnetic bodies are alternately arranged in the circumferential direction has been proposed.
A conventional rotor in which the magnets and the cores are alternately arranged in the circumferential direction is disclosed in, for example, Japanese Patent Application Publication no. 6-245451. The rotor in the Japanese Patent Application Publication no. 6-245451 includes six permanent magnets arranged at substantially equal intervals around a rotating shaft and six laminated core members which are respectively arranged between the respective permanent magnets and respectively forming magnetic poles (See, for example, the abstract and FIG. 1 of Japanese Patent Application Publication no. 6-245451).
As described in Japanese Patent Application Publication no. 6-245451, in a rotor core formed of laminated steel plates, a plurality of thin plate cores are bonded by a caulking operation (See, for example, the abstract and FIG. 3 of Japanese Patent Application Publication no. 6-245451). In addition, in order to further enhance the rigidity of the rotor core, it is preferable to provide a cylindrical core inside a plurality of cores arranged in the circumferential direction. However, when the cylindrical core is provided, it is difficult to firmly fix the plurality of thin plate cores only by performing caulking of the plurality of cores on the outside.
In particular, recently, an oil pump or a cooling fan has been reduced in size. Accordingly, a need for reduction in size of the inner rotor type motor used in such equipment has also increased. When the inner rotor type motor is to be reduced in size, it is more difficult to secure a region for performing caulking in the rotor core.